Liquid gas refrigeration system



March 26, 1968 H. L. BOESE 3,374,640

LIQUID GAS REFRIGERATION SYSTEM Filed Jan. 12, 1966 Fig.|

INVENTOR Harold L. Boese BY 75% wad ATTORNEY United States Patent3,374,640 LIQUID GAS REFRIGERATION SYSTEM Harold L. Boese, Duncanville,Tex., assignor to Boese Corporation, Dallas, Tex., a corporation ofTexas Filed Jan. 12, 1966, Ser. No. 520,254 22 Claims. (CI. 6252)ABSTRACT OF THE DISCLOSURE This invention relates to a refrigerationsystem utilizing a liquid gas as a cold reservoir. A vaporizer isemployed to convert the liquid gas to a vapor in which form it is passedthrough a set of cooling coils across which a ventilator forces a flowof air. The vaporizer is disposed remote from the air flow to preventerratic operation, and in a preferred embodiment, the volumes of thevaporizer and cooling coils are substantially equal to equalize thevapor pressures Within the system.

It is commonly known that conventional refrigeration and airconditioning systems which utilize compressors are complex, expensiveand require considerable maintenance. Conventional systems which do notuse a compressor, such as gas air conditioners employing the heat pumpeffect, are also expensive for other reasons. Moreover, both of thesetypes of systems comprise a relatively large amount of hardware andparts. Thus it is apparent that an air conditioning or refrigerationsystem in which the initial cost is low, which is economic to operateand which is greatly simplified in terms of the amount of equipment andparts used, has many advantages over more conventional systems.

Several attempts have been made to provide a simplitied and inexpensivesystem to replace the more conventional compressor type and gas-heatpump type systems by using an available cold reservoir, such as Dry Iceor liquid gas. However, none of these systems have met with any degreeof success for one or more reasons, as evidenced by the lack ofcommercially available units. Suffice it to say that a system that usesDry Ice as a cold reservoir is impractical because of the volumesrequired for storage, the fact that conduction to or from the coldreservoir takes place by means of carbon dioxide in the gaseous form,which is a poor conductor, and the fact that no means have been devisedto conserve the Dry Ice. Insofar as liquid gas reservoir systems areconcerned, no effective system has been devised that provides the degreeof cooling required in conjunction with a sufiicient conservation of theliquid gas. Moreover, no such liquid gas system has been devised thatprovides the necessary degree of control both as to temperature of thevolume or space to be refrigerated and as to the use of the liquid gasitself.

The use of a liquid gas for refrigeration purposes is desirable,however, because of its now availability in commerial quantities at lowcost, its large gas to liquid volume ratio for providing storage in asmall space in the liquid form and the very low temperature of the gasin the liquid form. Be this as it may, liquid gas is difficult to handleand control by virtue of the latter two characteristics just noted. Afew observations regarding the desirable features which a refrigerationsystem which uses a liquid gas reservoir will be informative when takenin conjunction with the problems of controlling the liquid gas.

Use of any liquid gas dictates that the vapor necessarily derivedtherefrom must eventually be discharged. It is not desirable todischarge this vapor directly into the space to be refrigerated forcooling purposes or otherwise, since there is inherently poorcirculation of the vapor for cooling purposes and it is normallyundesirable to fill this space with this vapor. Moreover, use of thevapor in the manner for cooling is inherently inefiicient in terms ofthe quantity of liquid gas used. If the vapor is discharged into thespace, a vent means must be provided to relieve the pressure build-up,thus creating an air conditioning leak. Even in circumstances Where itis not objectionable to discharge the vapor into this space, a suitablecirculation means should be provided for forcing a flow of air across aset of coils which are cooled by the liquid gas vapor.

Because of the tremendous pressures developed when liquid gas isconverted to a vapor, it will be apparent that controlling the vapor andthus the temperature of the space to be refrigerated, presents unusualproblems, both engineering and otherwise. Consequently, an efiicientvaporizer is necessary to provide an effective control over the gas inboth the liquid and vapor forms, which also implies an effectiveefliciency control. Moreover, an effective control over the vapor, orrate at which it is derived from the source of liquid gas, also impliesan effective temperature control of the space to be refrigerated. In theprovision of an effective and controllable vaporizer, it is alsoundesirable that the vaporizer be situated in any substantial heatexchange relation with the flow of air that is forced across the coolingcoils for circulation, since this would be a factor causing at least apartial loss of control over the vaporization process. There are otherconsiderations that must be taken into account in the use of a liquidgas reservoir to provide an effective refrigeration system, but theabove noted factors are of prime consideration.

The present invention has as a broad object thereof the provision of anair conditioning or refrigeration system which utilizes a liquid gasreservoir, wherein the system is both economical in cost and inoperation. Further, it is another object to provide such a system thathas application to virtually all air conditioning and refrigerationneeds. Accordingly, the present invention provides a system utilizing areservoir of liquid gas in which vapor is derived from the gas at acontrolled rate and passed through a set of coils across which airwithin the space to be refrigerated is forced to provide the necessaryrefrigeration. Preferably, liquid nitrogen is used because of itscommercially available quantities at low price, its low temperature inthe liquid state and its large gas to liquid volume ratio. Theconservation of the liquid gas is of primary importance in providing foreconomical operation while still providing for all the cooling powerthat is needed. To effect this, the system employs a vaporizer for theliquid gas that controls the amount of vapor used in accordance with thevolume and cooling requirements of the cooling coils.

Another object is to utilize, to the greatest degree possible, theliquid gas and vapor therefrom for additional functions other than forits cooling effect, While providing a system in which the refrigerationcan be controlled as desired. When a liquid gas is enclosed, aconsiderable vapor pressure will develop which, if not used forrefrigeration, must be released. In most refrigeration applications, thesystem will cool the space to be refrigerated to a temperature belowwhich it is not desirable to cool, in which case, the system'is cut backto control the space at this temperature. This means that less vaporfrom the liquid gas is needed for refrigeration, and consequently, thisvapor is available for other useful work. Moreover, it has been foundthat there is quite often more available vapor from the liquid gas thanis required for the refrigeration function. To utilize this additionalvapor, the invention also provides, in an embodiment thereof, acompletely automatic and self-contained system in which the vapor fromthe liquid gas is also used as a power source for operating other partsof the system in addition to its refrigeration functionl Specifically,an air driven ventilating fan means is employed which operates from thepressure of the vapor derived from the liquid gas. Moreover, the system,in another embodiment, is automatic in that various fiow rates of theliquid gas and vapor therefrom are controlled by valve means in responseto the temperature of the space to be cooled. In addition, a gas storagemeans is provided in communication with the liquid gas reservoir torelieve the vapor pressure therefrom for later use to perform usefulwork other than refrigeration.

- Many other objects, features and advantages will become readilyapparent from the following detailed description of the invention whentaken in conjunction with the 7 appended claims and attached drawing,wherein:

FIGURE 1 is a schematic diagram of a preferred embodiment of therefrigeration system of the invention; and

FIGURE 2 is'anelevational view in section of an air drivenv motoradapted for operation from a source of pressurized vapor from a liquidgas.

The system, as shown in FIGURE 1, comprises a container for containing aquantity'of a liquid gas, which container is comprised of any suitablematerial, such as metal, and which is suspended within an insulatedouter container 12 and insulated therefrom by a vacuum space 14.Container 12 is any suitable vacuum type container having insulatedwalls, wherein a preferred insulation for .the wallsis pearliteaggregate having an ASTM specification of C--57T, although any othersuitable insulation can be used. A pipe is provided to the reservoir 7and communicates with the vacuum space between the inner and outercontainers for pulling a vacuum within the space by any suitable vacuummeans or pump (not shown) through a pipe 36 connected to pipe 40through'a hand valve 38 and a suitable vacuum gauge 42 provided in line40 to monitor the vacuum. Line 40 is sealed within the outer containerby a vacuum seal. Another pipe or conduit 24 communicates with the coldreservoir and passes through the outer container by a vacuum seal andinto the interior of the inner container, also by a vacuum seal. Thisconduit extends down near the bottom of the inner container and is openon that end, and serves the dual purposes of filling the inner containerwith the liquid gas and drawing off liquid gas from the reservoir foruse as a refrigerant. Connected in communication with this con- .duit isa fill pipe 20 by means of another hand valve 22.

Another conduit 30 communicates with the interior of the reservoir andis passed through the walls of the inner and outer containers, as shown,by vacuum seals. This conduit has, as one purpose, the provision of atank exhaust means and is connected through a pressure gauge 32, asafety, pop-off valve 34and through a hand valve 28 to pipe 26, thelatter of which is open to the atmosphere.

pipe 20 while hand valves 22 and 28 are open, all as will be explainedbelow. An extension of conduit 24 is connected through a hand valve 52and a solenoid valve 54 to a set of coils'56 wound around the innercontainer 10 in heat conduction relationship therewith, whereby anotherextension 58 connected to the bottom of the'set of coils is connectedtoone side of another solenoid valve 60. The other side of valve 60 isconnected into a vaporas a cooling fluid.

Another pipe '68 communicates with the interior of enclosure 62 of thevaporizer and is connected to the input of a set of cooling coils acrosswhich air is forced to coolthe space to be refrigerated. The output ofthe cool-' ing coils 70 is then connectedto communicate with a gasstorage tank 78 by means of apipe 72 connected at one side to anothersolenoid valve 74 and pipe '76 connected at the other side of thesolenoid valve and into the storage tank. The storage tank, to befurther explained, is adapted to store the cold vapor passing throughthe cooling coils for acting as a power source for driving an air or gasdriven motor. A suitable pressure gauge and safety, pop-off valve 82 isprovided to the storage tank for monitoring the pressure and maintainingit at a safe level. A ventilating fan and motor- 86 is used to draw airacross the cooling coils for circulating the cold air within the spaceto be refrigerated. In the preferred embodiment, the ventilating fan andmotor comprises an air driven motor specially adapted for use with acold gas as will be explained in conjunctionwith FIGURE 2,

' and is connected to the top of the storage tank by means of a conduit84 passing through a pressure valve 85 and another solenoid valve 83.Valve 85 serves to automatical- 'above a predetermined minimum and tomaintain't'he pressure of the vapor in the top of the inner reservoirtank 10 below a predetermined maximum. This is not just for safetypurposes in so far as the reservoir tank is concerned, but allows asufiicient pressure to be maintained within the storage tank forproviding the required power for the system. To effect such a pressuredistribution, the

inner reservoir tank 10 and the storage tank 78 are con solenoid valve60 by means of another cross-coupling 98.

All of the solenoid valves mentioned are thermostatically operated inthe preferred embodiment of the invention for automatic control. Onemeans for accomplishing this, as shown in FIGURE 1, comprises athermostat located in heat conduction relationship with the cooling'coils 70 to monitor the temperature thereof, wherein the temperature ofthe cooling coils is proportional to the temperature of the volume orspace to be refrigerated.

. Thermostat 100, in one embodiment, is a conventional,

The inner container 10 is filled with the liquid gas through atemperature operated off-on switch connected at one side 7 to a batteryor voltage source 106 through electrical connection 102 and at the otherside by connection 104 to one terminal each of the four solenoids 74,54, 60 and 92 through electrical connections 112, 116, and 124,respectively. The other side of the battery or voltage source isconnected to the other terminals of the solenoids 74, 54, 60 and 92 bymeans of electrical connections 110, 114, 118 and 122, respectively. Itwill be remarked at this time that, in the particular embodiment shownand for the particular operation to be described, solenoid 92 isnormally open, whereas each of solenoids 54, 60 and 74 are normallyclosed. {That is to say, solenoid'92 can be spring biased to an opencondition which closes only upon the application thereto of a suitablevoltage to close it, wherein the solenoid valve opens again when thevoltage signal is removed. In contrast to this, the operation of theother solenoids are the opposite. Moreover, solenoid 83, althoughconnected to a different thermostat control, is also normally open. i

. The operation of this system, including the various features thereof,will now be described. The reservoir tank is initially, filled Withalliquid gas for operation. To accomplish this, hand valves 22 and 28are opened and hand valve 52 is closed. It will be assumed, of course,that a vacuum has already been established between the inner and outercontainers of the reservoirqA liquid gas is then pumped throughconnection into the interior of inner tank 10, and the fumes or vaporresulting from the filling of the tank are permitted to exhaust throughconduit 30 and out connection 26 through open valve 28. If the exhaustpath is not provided, it would be very difficult, if not impossible, tofill the tank to the desired quantity. Hand valve 52 is maintainedclosed during this time so that vapor pressure within the top of theinner tank 10 will not force the liquid gas back up through the systemprior to the time that operation is desired. The vapor within the top ofthe reservoir tank, however, can travel through cross-connection 96 andconduits 94 and 90 down into the storage tank, since valve 92 isnormally open. There is no objection to this since the purpose of thestorage tank is to store vapor at all times. The vapor can not enterinto the vaporizer through solenoid 60 at this time as the latter isclose-d. Once the reservoir has been filled to the desired quantity ofliquid gas, solenoid valves 22 and 28 are closed and solenoid valve 52opened. The system can then be left in this condition for apredetermined period of time to permit vapor to pass into the storagetank 78 through conduit 90 until a predetermined pressure is attained.At this time, the system can be actuated by closing a main switch 105connected between the battery and thermostat 100 to actuate solenoidvalves 74, 54, 60 and 92 in response to the temperature of the coolingcoils.

The temperature of the cooling coils will initially be at a relativelyhigh temperature, thus causing normally open solenoid 92 to close andnormally closed solenoids 54, 60 and 74 to open. The pressureestablished within the inner tank 10 as a result of vapor boiling fromthe liquid gas Will force the liquid gas by perculator action up throughconduit 24, through hand valve-52 and solenoid 54 and down through thelength of conduit 56 forming a coil about the inner reservoir tank inheat conducting relationship therewith. The passage of liquid gasthrough coil 56 acts as an additional thermal shield for the reservoir,whereby it should be understood that conduit 56 is not absolutelynecessary and can be obviated if desire-d. The liquid gas passes throughconduit 58 and open solenoid 60 into the vaporizer, wherein the liquidgas is vaporized or atomized as it passes through holes 66. The gas, nowin a vapor form, passes into the cooling coils 70 through conduit 68 andon into storage tank 78 through open solenoid valve 74. The vaporpressure from storage tank 78 causes the ventilating fan 86 to be drivenby the passage of the vapor therethrough. By this means, air is drawnacross the cooling coils to cool the space to be refrigerated. As thetemperature of the air of the space to be refrigerated drops and as thetemperature of the cooling coils drops in accordance therewith,thermostat 100 will open at a predetermined temperature to closesolenoid valves 54, 60 and 74 and to open solenoid valve 92. This is thetemperature at which sufiicient cooling is provided so that a continueddrop in temperature is not desired. However, it is important to maintaincirculation of the air within the space to be cooled, and thus theventilating fan 86 continues to run. This is provided by the pressurefrom'the storage tank 78. Furthermore, since liquid gas is no longerbeing derived from the reservoir at this time, it is necessary torelieve the vapor pressure within the top of the inner tank. Moreover,the pressure within the storage tank 78 will tend to drop as it is notbeing supplied through the cooling coils. To provide a stabilizationbetween the two tanks, the vapor passes from the liquid gas reservoirthrough cross-connection 96 and down into the storage tank through opensolenoid valve 92. Thus a continuous source of pressure is provided forrunning the ventilating motor 86.

Cross-connection 98 is provided between the top of the reservoir tankand the input to the vaporizer to further relieve the pressure from theliquid reservoir when solenoid valve 92 is closed, so that an excessiveamount of pressure will not build up within the liquid reservoir whenthe system is circulating the liquid gas. That is to say, -a releasepath is provided should the pressure within storage tank 78 tend toexceed a maximum during operation of the system. Pressure valve isprovided in conduit 84 to maintain a constant flow rate of vapor throughmotor 86. This pressure valve is of any suitable design and is automaticin that it opens and closes according to the pressure applied theretofrom storage tank 78.

Vaporizer 62 plays a very important functional role in the operation ofthe system. It will be noted that in the preferred embodiment shown, theliquid gas is converted to a vapor primarily by an atomization processrather than by heating the liquid gas, although heating does play apart. The vaporizer is at a higher temperature than the liquid gasitself, and thus the higher heat does aid the atomization process.However, the heat transferred to the vaporizer from its surroundings issubstantially constant, so as not to vary the rate of vapor formationthat is controlled. It is highly undesirable that the vaporizer besituated within the air flow created by ventilator 86, since this willeffect the control and cause substantially greater heating of the vaporand its rate of creation. This, of course, is because of the heatexchange relation that would exist between the vaporizer and the highvelocity air stream. It is much more desirable to have the liquid gasvaporized at as low a temperature as possible, transfer the vapor to thecooling coils, and effect all the necessary refrigeration of the spaceby an air flow across the coils. Since the vapor flow through the coilsmust be stopped from time to time to maintain the exact temperaturecontrol desired, means must be provided to perform this function, andthis is effected by the solenoid valve 60'. It will be remarked thatpressure within the vaporizer will exceed the pressure within thereservoir tank because of the higher temperature. If valve 60- weredisposed between the vaporizer and the cooling coils in conduit 68, theincreased pressure would back up into the reservoir tank when the valveis closed. Consequently, a tremendous rush of vapor, and even the liquidgas itself, would be pushed through the cooling coils when the valve isreopened because of the pressures involved. The liquid gas would nothave time to become vaporized because of the velocity with which itwould travel from the reservoir tank to the coils. Consequently anexcessive amount of liquid gas would be used and wasted, in addition toan almost complete loss of temperature control and regulation. Bysituating valve 60 between the reservoir and vaporizer, the increasedpressure is blocked within the vaporizer and not allowed to back up intothe reservoir. In effect then, the flow of liquid gas itself is directlycontrolled to effect an indirect control over the flow of vapor. Thesystem just described is capable of continuous operation for aconsiderable length of time before it becomes necessary to replenish theliquid nitrogen (or other gas) supply. Liquid nitrogen is preferredbecause of its commercial availability at low cost of about four cents(4c) per pound, its large gas to liquid expansion ratio and its lowtemperature of 320 F. in the liquid state. To illustrate the capacity ofthe system, and typical operating temperature and pressures, as oneexample only, a liquid nitrogen reservoir tank having a capacity to hold97 pounds of liquid nitrogen when full is typical for refrigerating arefrigeration truck. The vapor pressure on the top is maintained atabout 100 pounds per square inch pressure absolute. Similarly, the vaporstorage tank is also maintained at about 100 pounds per square inchpressure and thus it will be seen that the storage tank acts as apressure equalizer for the reservoir tank. It will be apparent that allthe liquid nitrogen within the reservoir above the bottom of outletconduit 24 will eventually be used. For safety purposes, the safetyvalves 34 and 82 are set to discharge at a pressure of about pounds persquire inch.

The volume of the vaporizer 62 is preferably equal to 7 the totalinterior volume of cooling coils 70, although diiferent volumes can beused. Should the volume of the vaporizer be larger than that of thecooling coils, a

layer of vapor pressure will exist in the vaporizer, thus causing thecooling coils to be operated at a lower tem perature than the vaporizerbecause of the increased vapor flow rate therethrough. Thermostat 100 isnormally set at 40 F. for refrigeration purposes (the air or space beingrefrigerated being at a higher temperature),

maintain the proper refrigeration temperature in a refrigerated truckvan of dimensions 40 ft. x 7.5 ft. x 7 ft., with a depletion rate of theliquid nitrogen of no greater than one pound per hour.

The system, as shown in FIGURE 1, can also be used to air condition thecab of a truck, for example, or heat the cab as desired. To efiect this,another set of cooling coils 130 is provided across which a flow of airis forced by a ventilator 133 within the cab. To provide the cooling forthe coils 130, a conduit 131 is connected to the outlet conduit 88 ofmotor 86 through a three-way valve 87. Valve 87, when turned as shown,connects conduits 88 and 131, but when turned 90 from that shownconnects conduit 88 with an atmosphere exhause pipe 89 and shuts offconduit 131. The latter valve position is used when no heating or airconditioning to the cab is desired. A pipe 132 connects the outlet ofcoils 130 to ventilator 133 for operation, the latter also being a gasdriven motor and fan' combination. The vapor is then discharged to theatmosphere through pipe 134.

For purposes of heating, a conduit 138 connects a set of heating coils137 wound about the truck muffler or other exhaust means 136 incommunication with the outlet conduit from the storage tank, as shown,through another solenoid valve 139. The other side of the heating coilsis connected in communication with conduit 84 preceding the input tomotor 86 by means of conduit 140.

each of solenoid valves 83 and 139 through electrical connections 146and .148, respectively, and the other thermostat terminal 144 isconnected to one side of battery 106. Theother terminals 145 and 147 ofsolenoid valves 83 and 139 are connected to the other side of thebattery.

When thermostat 142 registers above a predetermined maximum temperature,solenoid valve 139 is closed, and valve 83 is open, thus allowing thecold vapor from the storage tank (which is suitably insulated) to passdirectly to motor 86 and into coils 130. If the temperature registeredby thermostat 142 falls below a predetermined minimum, valve 83 Will beclosed and valve 139 opened, thus directing the vapor from the storagetank through the heating coils 137 before it passes through motor 86 andcoils 130. It will be apparent that cold vapor passing through coils 130will be at a higher temperature than when the vapor passes through coils70, primarily because of the heating effect on the vapor in the latter.However, this is desirable since it is normally not desired torefrigerate the cab of the truck to the degree that the van isrefrigerated. Even so, the vapor temperature is more than adquately lowto provide all the cab refrigeration required. In so far as the heatingof the cab is concerned, it will be apparent that the vapor from thestorage tank provides a readily available medium for transferring heat 8from the exhaust means 136 to coils 130. Without this vapor supply, anair intake system, or water system, would be required.

An elevational view in section of an air driven motor adapted for usewith the system as the ventilating means is shown in FIGURE 2. It willbe remarked that a conventional air driven motor cannot be used withthis system because of the low temperature of the vapor that is used todrive it, although suitable modifications can be made to adapt it forthis use. The motor comprises a housing 150 which defines a central,cylindrical cavity 151 having a cylindrical wall surface 152. Thehousing is mounted on a base 154 for mounting the motor. A cylindricalrotor 156 is provided which is mounted eccentric of the central axis ofthe housing on an axle 158 mounted at either end in conventionalbearings (not shown). A set of vanes 160, 162, 1-68 and 170 are providedwithin the rotor, which vanes are elongated and substantiallycoextensive with the length of the rotor along the axis thereof andmounted within suitable channels. Vanes 160 and 162 are eachspring-biased outwardly by springs 165 and 166, respectively, whichsprings bear against the inner ends of the vanes and bear against theopposite ends of a pusher rod 164 at the other ends. The pusher rod isfree to move along the line connecting the two vanes as required by thepressure exerted by the springs. The outer ends of the vanes are curvedto provide a smooth interface with the inner surface 152 of the motorhousing. Vanes 168 and 170 are similarly mounted on the opposite ends ofanother pusher rod 172 through springs 173 and 174, respectively,wherein this pusher rod is also free to move along the line connectingthe two vanes as determined by the spring pressures. The pusher rods 164and 172 are nonintersecting for obvious reasons.

A first channel or cavity is provided in the motor housing at one sideof the rotor and communicates with a pipe or conduit 184, so that air orother gas may be supplied through the pipe to the intake 180 of themotor. Similarly, another channel or cavity 182 is provided at the otherside of the rotor and communicates with another pipe 186. This motor, asappears from the drawing,

can be driven in either direction with pipe 184 being used as the inputand pipe 186 used as the output, or vice versa. Assuming that air underpressure is applied through pipe 184, the-air pushes against the vanesto cause the rotor to turn in a counter clockwise direction as viewed inFIGURE 2. The rotor is mounted eccentric to the axis of the motorhousing so that a pressure differential or build up will be created asthe rotor rotates to compress the air on the right side of the rotorwhen turning in a and the vanes are dissimilar, and consequently havedifferent thermal coeflicients of expansion and contraction.

'Even if the rotor and vanes are comprised of the same metal, thetolerances that would have to be maintained would be too severe becauseof the relatively large thermal coefficients of expansion of mostmetals. To eliminate this problem, the rotor and vanes are manufacturedof the same material which has a very low coeificient of thermalexpansion and contraction. In the preferred embodiment, both the rotorand vanes are comprised of Teflon, which is commonly known and is atrade name of the Du Pont Company. This material, in addition to havinga low thermal coefiicient of expansion and contraction, is well adaptedfor the use to which it is applied in the rotor.

Consequently, the motor cannot freeze up even at the low temperaturesinvolved.

Many modifications and substitutions of the invention will undoubtedlybecome apparent when taken in conjuction with the preceding descriptionthereof. However, it is intended that all such modifications andsubstitutions that fall within the true scope of the invention beincluded therein, and that the invention be limited only as defined inthe appended claims.

What is claimed is:

1. A refrigeration system comprising:

(a) a source of liquid gas,

(b) a set of cooling coils through which vapor from said liquid gaspasses,

(c) a ventilator for forcing a flow of air within a space to be cooledacross said cooling coils, and

(d) a vaporizer situated in substantially non-heat exchange relationWith said flow of air and said space to be cooled connecting said sourceof liquid gas with said set of cooling coils for supplying said set ofcooling coils with a flow of vapor from said liquid gas therethrough.

2. A refrigeration system according to claim 1 including an enclosedcontainer for containing said liquid gas under vapor pressure, and aconduit connecting said source of liquid gas with said vaporizer havingan open end communicating with the interior of said container beneaththe liquid level of said liquid gas and arranged so that liquid gas isfreed therethrough against the force of gravity by said vapor pressure.

3. A refrigeration system according to claim 2 wherein said vaporizercomprises an enclosed space which communicates with said set of coolingcoils and an atomizer coupled to said conduit and disposed within saidenclosed space through which said liquid gas passes and is converted toa vapor.

4. A refrigeration system according to claim 1 wherein said ventilatorcomprises a gas driven ventilating fan means communicating with theoutlet of said set of cooling coils for being driven by the vaporpassing through said set of cooling coils.

5. A refrigeration system according to claim 3 wherein the interiorvolume of said enclosed space is substantially equal to the interiorvolume of said set of cooling coils.

6. A refrigeration system according to claim 1 wherein said liquid gascomprises nitrogen.

7. A refrigeration system according to claim 2 wherein at least a partof said conduit is disposed in heat exchange relation with saidcontainer.

8. A refrigeration system according to claim 1 including control meansdisposed intermediate said source of liquid gas and said vaporizer forregulating the flow of liquid gas to said vaporizer.

9. A refrigeration system according to claim 4 including a gas storagetank disposed intermediate and in communicating relationship with saidset of cooling coils and said ventilating fan means.

10. A refrigeration system comprising:

(a) a container for containing a liquid gas,

(b) a vaporizer for converting liquid gas to a vapor,

(c) a first conduit having an open end communicating with the interiorof said container beneath the liquid level at which said liquid gas isto be maintained and communicating at the other end with said vaporizer,through which liquid gas is forced by the vapor pressure created in thetop of said container,

(cl) a set of coils communicating at an inlet thereof with saidvaporizer through which said vapor passes,

(e) a gas storage tank,

(f) a second conduit connecting the outlet of said set of coils withsaid gas storage tank for containing the vapor passing through said setof coils,

(g) a third conduit connecting the top of said liquid gas container withsaid storage tank,

(h) a gas driven ventilating fan means communicating with said gasstorage tank for being driven by the vapor contained within said storagetank for forcing a flow of air within a space to be cooled across saidcooling coils,

(i) first, second and third controllable valve means disposed withinsaid first, said second and said third conduits, respectively, and

(j) control means connected to said first, said second and said thirdvalves responsive to the temperature of said set of coils forcontrolling said first, said second and said third valves means.

11. A refrigeration system according to claim 10 wherein said controlmeans causes said third valve means to close when said first and saidsecond valve means are caused to be opened thereby, and vice versa.

12. A refrigeration system according to claim 10 wherein said first andsaid second valve means are normally closed and said third valve meansis normally open, and said control means causes said first and saidsecond valve means to open and said third valve means to close when thetemperature of said set of coils exceeds a predetermined minimum,whereby said third conduit provides a path for the flow of vapor fromsaid liquid gas container to said storage tank when said first and saidsecond valve means are closed and said third valve means is open tomaintain the vapor pressure within said liquid gas container below apredetermined maximum and said vapor pressure within said storage tankabove a predetermined minimum.

13. A refrigeration system according to claim 12 including a fourthconduit connecting said storage tank with said ventilating fan means,and fourth valve means disposed within said fourth conduit formaintaining the flow rate of vapor to said ventilating fan meanssubstantially constant.

14. A refrigeration system according to claim 13 wherein each of saidfirst and said second valve means comprises a normally closed solenoidvalve, said third valve means comprises a normally open solenoid valve,said fourth valve means comprises a pressure regulator, and said controlmeans comprises a source of electrical power for operating said first,said second and said third valve means and thermostat means forconnecting said source of electrical power thereto when the temperatureof said set of coils exceeds said predetermined minimum.

15. A refrigeration system according to claim 10 including a fourthconduit connecting the top of said liquid gas container with said firstconduit.

16. A refrigeration system according to claim 10 including a fourthconduit connecting said third conduit with said first conduit, whereinsaid first valve means is disposed within said first conduit between theinterconnection of said first and said fourth conduits and saidvaporizer, and said third valve means is disposed within said thirdconduit between the interconnection of said third and said fourthconduits and said storage tank.

17. A refrigeration system according to claim 1 including an additionalset of cooling coils, means for passing the vapor passing through saidfirst mentioned set of coils through said additional set of coils, andan additional ventilator for forcing a flow of air across saidadditional set of cooling coils.

18. A refrigeration system according to claim 10 including an additionalset of coils communicating at an inlet thereof with the outlet of saidventilating fan means through which said vapor passing through saidventilating fan means passes, and an additional gas driven ventilatorfan means communicating with the outlet of said additional set ofcooling coils for being driven by said vapor for forcing a flow of airacross said additional set of cooling coils.

19. A refrigeration system according to claim 10 including an additionalset of coils, a fourth conduit connecting said gas storage tank with aninput of said ventilating fan means to provide said communicationtherefor, a fifth conduit connecting an outlet of said ventilating fanmeans with an inlet to said additional set of coils through which saidvapor passing through said ventilating fan means passes, a sixth conduithaving an inlet and an outlet and adapted to' be disposed in heatconducting relationship with a source of heat interconnected at bothsaid inlet and said outlet thereof with one of said fourth and saidfifth conduits,'means for controllably directing said vapor which passesthrough said additional set of coils through said sixth conduit, andadditional gas driven ventilating fan'means communicating with theoutlet of said additional set of coils for being driven by said vaporfor forcing a flow of air across said additional set of coils.

20. A refrigeration system according to claim 19 wherein said means forcontrollably directing said vapor through said sixth conduit comprises afourth controllable valve means disposed within said sixth conduit and afifth controllable valve means disposed in said one of said fourth andsaid fifth conduits between said inlet and said outlet of said sixthconduit.

12 7 21. A refrigeration system according to claim 1 wherein said vaporpassing through said set of cooling coils is discharged remote to saidspace to be cooled.

22. A refrigeration system according to claim 10 wherein said vaporpassing through said ventilating fan means is discharged remote to saidspace to be cooled.

, I References Cited UNITED STATES PATENTS 1,905,811 4/1933 Culver 624402,718,766 9/1955 Imperatore et al. 62-434 2,943,459 7/1960 Rind 6252 r3,058,317 10/1962 Putman 62-52 3,092,976 6/1963 Tafreshi 6298 3,191,3956/1965 Maher et al. 62--52 3,241,329 3/1966 Fritch et al. 62-523,255,597 6/1966 Carter 62-239 3,271,970 9/1966 Berner 62-419 LLOYD L.KING, Primary Examiner.

